Microphone



Feb. 11, 1930. Q VON 1 1 1,746,449

MICROPHONE Filed NOV. 24, 1925 INVENTOR OTTO VON BRUNK BY Q TORNEY 1 Patented Feb. 11,1930

' OTTO VON BRONK,

. the photo-electric type and one of theob of my. invention is to produce a microp one vention will appear more fully as hereinafter UNITED STATES PATENT OFFICE MICROPHONE or BERLIN, GERMANY, ns'srenon T0 eEsELLscnArr r 'ctn nnm'rnosn 'rELnenArHIn M. 1;. BL,

OF BERLIN, GERMANY Application filed November 2 t, 1925, Serial No. 71,064, and in Germany November 29, 1924. A

This invention relates to a microphone of ects wherein no diaphragm is used with a conseqllent' elimination of the distortional defects hitherto attendant upon the use of microphones of the diaphragm type.

Another object of my invention is to provide a microphone wherein variations in the intensity of a light source are brought about by the direct action of sound waves with a subsequent conversion of the light variations into electrical oscillations.

Still another object of my invention is, to provide a method of translating sound waves into electrical variations which consists in subjecting a conductor to a constant flow of electric current whereby the conductor is heated to emit light, directing sound waves on saidconductor to cause variations in the intensity of the emitted light, subjecting a light sensitive cell to the light variations, and passing an. electric current through the cell whereby said latter current varies in accordance with said light variations.

Other objects and advantages of my in set forth.

In. the present invention a source of light oscillations is influenced directly by the action of sound waves and these variations of light intensity acting upon a photo-electric cell, e. g., a selenium cell or an alkali-cell, produce resistance changes in an electric circuit,

7 whereby the sound waves are converted into electric current variations of a correspond ing value.

In the drawing herewith the idea underlying the invention is shown:

Fig. 1, is a cross section of an insulation frame 1 made of refractory material on which a number of thin wires (which may be platinum wires) are conductively connected with terminal screws 3 and 4. These wires may be raised to white incandescence by electrical currents of suitable intensity.

Fig. 2, is an arrangement wherein the light rays emanating from the incandescent wires are received by a photo-electric cell 5, the va- 1 riations in current of which are fed to the grid of a thermionic valve in the usual manner.

Since in the photo-electric microphone no diaphragm is used, the effect, in contradistinction to the diaphragm type of microphone heretoforeused isfree from distortion. In order "tomagnify the intensity of the sound waves a convenient plan is to mount a funnel. 6 (a megaphone)" on the microphone as shown in Fig. 2.

i It will be understood that the arrangement and method hereinbefore set forth may be varled, and that the general principles disclosed may be embodied in other organizations widely different from those illustrated without departing from'the spirit of my invention or the scope of the appended claims.

What I claim is new and desire to secure I I pendentl of the flow of current through said wire, an means to translate the light variations into electric oscillations whereby an indicating circuit may be functioned.

' 3. In a microphone of the photo-electric type'a light source consisting of a plurality of wires, means for causing a constant current to fiow through said wires whereby they are maintained at incandescence, means to directly var the intensity of the light emanating from t e incandescent wires without varying the flow of current therethrough and means'to translate the light variations into electric oscillations whereby an indicating circuit may be operated.

4. In a microphone of a photo-electric type a light source consisting of a plurality of wires, a source of direct current energy for maintaining said wires incandescent, means for causing sound waves to vary the intensity of the light emanating from the incandescent wires without varying the flow of current through said wires, a photo-electric cell responsive to said variations of light intensity and a thermionic valve associated with the photo-electric cell, whereby an indicatingcircuit may be 0 rated.

10 5. The met 0d of translating sound waves into electric oscillations which consist in providin electrically a source of: 1i ht, directing soun waves'on said source of 'ght to cause variations in its intensit directly afiecting u a light sensitive cell wit the varying light waves from said source of light and continuously passing'afi electric current through said cell, whereby said current oscillates in accordance with the resistance changes of said cell.

6. A microphone comprising an insulatin frame, terminals on opposite sides of sa1 frame, a plurality of fine wires stretched between said terminals, means for maintaining a said wires at incandescence, a megaphone adjacent one side of said frame, and a light sensitive cell adj acent the opposite side of said frame, said cell being connected in an electric circuit, whereby the sound waves collected 3 in the mega hone are translated into electric oscillations 1n said circuit.

7. A'method of translating sound waves into electrical variations WhlChCOIlSlSlZS in subjecting a conductor to a constant flow of 35 electric current whereby the conductor is heated to emit light, directing sound waves on said conductor to cause variations in the intensity of the emitted light, subjecting a light sensitive cell to the light variations, and

passin an electric current through the cell where y said latter current varies in accordance with said light variations.

OTTO VON BRONK. 

